1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to disk drives having a voice coil motor that is configured to selectively assume a first configuration that can generate a first maximum torque and assume a second configuration that can generate a second, higher maximum torque.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a slider with at least one transducer or read/write element for reading and writing data. A Voice Coil Motor (VCM) exerts torque on a rotary actuator to move the HSA over the disk. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. The slider or head including the drive's read/write transducers is said to be “flying” over the disk when in this state.
Competitive pressures continue to drive the disk drive industry to seek ways to market ever higher performing drives. One of the more competitively important drive metrics is the track access time. The track access time is the time the read/write heads of the actuator assembly take to travel from their present track to a destination track on the disk surface. To reduce the actuator track access time (i.e., to make the actuator assembly move faster) using a conventional VCM requires increasing the magnet volume, increasing the number of coil wire turns and/or increasing current input to the coil to generate increased torque. Each of these alternatives has drawbacks. Increasing the magnet volume requires a corresponding increase in the volume of the magnet back irons, and the extra space needed for such increases may not be available in the drive enclosure. Increasing the number of coil turns may unacceptably increase the actuator inertia and may detrimentally reduce the butterfly mode frequency of the actuator. Lastly, the current to the coil may not be arbitrarily increased, as the maximum current that may be input to the coil depends on the available voltage as well as the total resistance of the coil. As the VCM is driven with ever-higher currents in an effort to reduce seek times, thermal dissipation in the VCM also becomes an important issue. Indeed, heat is generated as the coil of the VCM is subjected to high coil driving currents and this heat must somehow be dissipated without damage to the drive.
From the foregoing, therefore, it is clear that improved disk drives are and will continue to be needed. In particular, higher performing drives are needed to drive the VCM's coil with higher input current to achieve faster seek times. Also needed are disk drives in which such fast seek times are achieved without overheating the VCM's coil.